Corrosion-endangered parts of apparatus used in alkali metal chloride electrolysis having protective covering of post-chlorinated pvc



April 1, 1969 K. HASS ET AL 3,436,324

CORROSION-ENDANGERED PARTS OF APPARATUS USED IN ALKALI METAL CHLORIDE ELECTROLYSIS HAVING PROTECTIVE COVERING 0F POST-CHLORINATED PVC Filed May 2. 1966 I-/- L I I7 INVENTORS KARL HASS WALTER KOLHAGEN GUNTHER CZEHOVSKY 7 BY HANS'EWALD KONERMANN ATTORNEYS.

US. Cl. 204-128 8 Claims The subject of the invention is the use of special types of post-chlorinated polyvinyl chloride as a coating material for corrosion-endangered parts of apparatus used in alkali metal chloride electrolysis.

It is in the prior art to manufacture out of metallic materials, conduits having a protective lining for parts of apparatus used in alkali metal chloride electrolysis, and to protect the surface with material that resists the action of the aggressive liquids and gases in the electrolysis cell, such as rubber or plastics for example. It is also in the prior art to use tubing and sleeves that are made wholly from ceramic or like material, such as porcelain and glass. Also known is the manufacture of the above-mentioned apparatus parts partially from solid plastics, and also in one layer or in a plurality of layers from plastics of various kinds with and Without mechanical reinforce ment by inorganic and organic fibrous materials. Disadvantages of the materials listed consist mainly in the fact that the coatings become separated from the structure covered, and also they often do not adequately resist the chemical attack.

Ceramic material generally offers quite good chemical resistance under the conditions of alkali metal chloride States Patent O percent, for example 64-70 wt. percent, and in which about to 90 wt. percent and preferably about to wt. percent of the additional chlorine introduced by post-chlorination is in 1,2-dichloroethylene units, can be used advantageously as coating material for corrosion-endangered parts of apparatus used in alkali metal chloride electrolysis.

The advantages of the use, according to the invention, of the described post-chlorinated types of PVC, lie both in the gOOd thermal stability and in the good resistance to breakage of such coatings, combined with outstanding corrosion resistance. The said coatings are furthermore susceptible of welding and cementing. They can also be cut and machined, even after application.

With the material described, corrosion-endangered tubing, covers for the power lines to the graphite anodes, lid coatings, bath and vat linings and other parts of alkali metal chloride electrolysis equipment can be coated, as well as other products.

The coating material of the invention may contain the conventional substances to improve workability. The semiproducts which are used for the manufacture of the coatings can be made by plastics manufacturing methods of the prior art.

The use according to the invention of the chlorinecontaining thermoplastics described is illustrated by the following examples:

Example 1 Used as protective tubing for the conductors connected to the graphite anodes of equipment used in sodium chloride electrolysis.

The conductors of the graphite anodes were covered with pieces of plastic tubing with a 4 mm. wall thickness and a 40 mm. outside diameter, and were exposed to the eliects of a sodium chloride electrolysis at the stated temperatures and times.

1a to lg: Examples for comparative purposes.

U: to 1i: Examples of the use of various types of post chlorinated PVC.

TABLE 1 Experiment Material Time Temp., Change State after Removal No. (days) C. in O.D.

1a Polyethylene (unfi ed) 60 83 +1. 5% Surface sinooth, ma y individual bubbles protruding as muc as 3 mm. 11) Polyethylene (stabilized with carbo black). 143 +2. 4% Surface irregular, with bumps up to 4 mm. beyond diameter. 10 .do 55 83 +9. 4% Surface textured; layer 0.6 mm. thick spalled ofi. 1d Polypropylene.-- 83 2. 5% Loss of substance due to spelling oil of thin layers 0.1 mm. thick. 1e -do 1 3 85 -1. 7% 0. 1f Polyvinyl chloride 126 84 +7. 5% Uniform thickening over entire surface subject to attack. Surface rough and brittle. d0 85 +2. 6% Do.

Polyvinyl chloride (post-chlorinated) 155 83 +0. 2% Surface uniformly smooth, unaltered. .d0 143 85 +0. 2% Do.

The post-chlorinated polyvinyl chloride used in Example 1 was produced as follows: A suspension PVC with a K value of 68 was brought up by post-chlorination to a chlorine content of 67.2%. 69% of the chlorine is disposed in 1,2-dichloroethylene units (the 1,2-dichloroethylene unit content was determined by measurement of the nuclear resonance spectrum). After the addition of 3 wt. percent of Ba-Cd laurate, 2 wt. percent of a lubricant commercially obtainable under the name of E-Wax and 0.5 wt. percent of calcium stearate, the material was extruded at C. into tubes of the specified size.

Example 2 Used as bath lining: 2a to 2b: Tests for comparison Use of a type of post-chlorinated PVC.

4 measurement of the nuclear resonance spectrum. This method is described in Ang. Chemie 77 (1965) pp. 1124- 34 by H. I. Harewood. The post-chlorinated polyvinyl chloride can be rolled at 170-190 C. The thermal sta- TABLE 2 Experiment No. Material Time Temp., Change in Findings (days) 0. OD.

2a- Fibercast (epoxy resin) sheet 40 83 6.4% Loss of material, crumbly surface. 21) Polyethylene sheet (stabilized with 35 78 +42% Surface textured, occasional closed carbon black) bubbles bleached.

2c Pagggigyl chloride sheet (post-chlorl- 30 75 +0. 04% Edges unaltered andsmooth surface.

The post-chlorinated PVC used in Example 2 was probility of the described material is superior to other known duced as follows: A suspension PVC with a K value (H. 15 types. Fikentscher Cellulosechernie, 13, 1932, p. 58) of 60 was The invention finds application for all processes wherein brought up by post-chlorination to a chlorine content of alkali chlorides are electrolyzed, and chlorine is produced. 65.8%. 75.5% of the chlorine was attached in units of While the invention has been described with respect to 1,2-dichloroethylene (the 1,2-dichloroethylene unit conparticular embodiments thereof, these embodiments are tent was determined by measuring the nuclear resonance 2O merely representative and do not serve to determine the spectrum). The material after the addition of 3 wt. perlimits of the invention. cent of Ba-Cd laurate, 1 wt. percent of titanium dioxide What is claimed is: and 0.5 wt. percent of Ca stearate, was rolled to a sheet 1. Electrolysis cell for electrolysis of alkali metal chlo- 0.5 mm. thick and then pressed into sheets 4 mm. thick ride comprising equipment adapted to contact said alkali at 190 C. 25 metal chloride and reaction products produced therefrom Thus, the invention provides an electrolysis cell for comprising a corrosive reaction environment including a electrolysis of alkali metal chloride comprising equipment tank for holding an alkali metal chloride bath for elecincluding a tank for holding an alkali metal chloride bath trolyzing, electrodes disposed in the tank, conduit for confor electrolyzing, electrodes disposed in the tank, conduit veyance of electrolysis material, and conductors connected for conveyance of electrolysis material, and conductors to said electrodes, at least part of said equipment being connected to said electrodes, and an alkali metal chloride susceptible to corrosion and having a protective covering bath for electrolysis in the tank. According to the invenconsisting essentially of post-chlorinated polyvinyl chlotion, a least part of the equipment is provided with a proride polymer. tective covering consisting essentially of post-chlorinated 2. Electrolysis cell according to claim 1, said post-chlopolyvinyl chloride polymer. rinated polyvinyl chloride having a chlorine content of The invention is further described in reference to the about 64-70 wt. percent, and about 50-90 wt. percent of accompanying drawing, wherein: the additional chlorine introduced by post-chlorination be- FIG. 1 is a schematic representation of an electrolysis ing in 1,2-dichloroethylene units. diaphragm cell according to the invention. 3. Electrolysis cell according to claim 2, wherein the A tank 1 is provided with a protective covering 2, and is cell is lined with said protective covering. outfitted with lid 10, which is provided with a protective 4. Electrolysis cell according to claim 3, wherein said covering 12. A sodium chloride brine bath 20 is contained conductors are protected with said protective covering. within the tank, and anode 4 and cathode 5 are immersed 5. Electrolysis cell according to claim 4, wherein said in the tank. The cathode is covered by a diaphragm 6. conduit is lined with said protective covering. The anode and the cathode are serviced by conductors in- 6. Electrolysis cell according to claim 2, wherein said snlated by a protective covering according to the invenconductors are protected wtih said protective covering. tion. The conductor 14 which is connected to the anode 7. Electrolysis cell according to claim 2, wherein said 4 is provided with protective covering 13; the conductor conduit is lined with said protective covering. 15 which is connected to the cathode 5 is protected by 8. A process for production of chlorine comprising protective covering 7. Bushings 3 and 9 are provided where electrolyzing alkali metal chloride in an electrolysis cell the conductors pass through the tank Wall and the wall thereby producing a corrosive reaction environment, said of the lid. These bushings can be formed of post-chloricell including equipment exposed to the corrosive reaction nated polyvinyl chloride according to the invention. Conenvironment, said equipment including a tank holding the duit 16 is provided for withdrawal of chlorine from the alkali metal chloride bath, electrodes disposed in the tank, cell, and is provided with a protective lining 17; similarly, conduit for conveyance of electrolysis material, and conconduit 8 is provided for withdrawing hydrogen from the ductors connected to said electrodes, at least part of said cathode, and is also provided with a protective lining (not equipment being susceptible to corrosion and having a proshown). The various protective coverings and linings mentective covering consisting essentially of post-chlorinated tioned are of post-chlorinated polyvinyl chloride according polyvinyl chloride polymer. to the invention.

FIG. 2 is a schematic representation of an electrolysis References Cited mercury cell according to the invention. UNITED STATES PATENTS The description, apart from constructural differences, corresponds with that given for FIG. 1, except that 4 g g -gg being the graphite anode and 5 the mercury cathode. 21 is for the introduction of the brine. OTHER REFERENCES The post-chlorinated polyvinyl chloride used in the in- Evans, Tank Linings, Metal Industry, July 29, 1949, pp. vention has a chlorine content of between about 64 and 86-88. wt. percent and in which about 50 to 90 wt. percent Evans, I.E.T.S., vol. 24, pp. 129-143, 1948-49. the additional chlorine introduced by post-chlorination is 70 in 1,2-dichloro-ethylene units. It can be produced by the procedure disclosed in the Belgian Patent 654,377, corresponding with our pending U.S.-application Ser. No. 403,949, filed Oct. 14, 1964, now Patent No. 3,362,896. The 1,2 dichloro-ethylene units can be determined by JOHN H. MACK, Primary Examiner.

D. R. JORDAN, Assistant Examiner.

U.S. Cl. X.R. 

8. A PROCESS FOR PRODUCTION OF CHLORINE COMPRISING ELECTROLYZING ALKALI METAL CHLORIDE IN AN ELECTROLYSIS CELL THEREBY PRODUCING A CORROSIVE REACTION ENVIRONMENT, SAID CELL INCLUDING EQUIPMENT EXPOSED TO THE CORROSIVE REACTIN ENVIRONMENT, SAID EQUIPMENT INCLUDING A TANK HOLDING THE ALKALI METAL CHLORIDE BATH, ELECTRODES DISPOSED IN THE TANK, CONDUIT FOR CONVEYANCE OF ELECTROLYSIS MATERIAL, AND CONDUCTORS CONNECTED TO SAID ELECTRODES, AT LEAST PART OF SAID EQUIPMENT BEING SUSCEPTIBLE TO CORROSION AND HAVING A PROTECTIVE COVERING CONSISTING ESSENTIALLY OF POST-CHLORINATED POLYVINYL CHLORIDE POLYMER. 